1. Field of the Invention
The present invention relates to a communication system, and a communication apparatus and a communication method thereof. More particularly, the present invention relates to a communication system performing communication over a mobile communication network and an internet network, and an apparatus and a method for providing a call state thereof.
2. Description of the Related Art
In general, Instant Messaging/Presence Service (IM/PS) means a service that provides state information for determining states of presentities such as physical positions, communication states, or communication media to watchers. Namely, in a communication system, watchers may determine states of presentities from the state information, and communicate with the presentities using respective User Equipments (UEs). In this case, the communication system provides the IM/PS through an internet network. Accordingly, to use the IM/PS by an UE, presentities and watchers should use an UE accessible to the internet network. Namely, the communication system provides states of the presentities through an internet network. However, the foregoing communication system has a problem that cannot determine states of presentities in a cellular network. For this reason, because the communication system does not provide state information of presentities over the cellular network, watchers cannot determine states of the presentities. For example, the watchers cannot determine communication states of the presentities, namely, presence of call execution. Accordingly, the watchers have a difficulty in communicating with the presentities using an UE.